1. Field of the Invention
The present invention relates to sealing materials (or sealants) for flip chip-type semiconductor devices, and more particularly to underfill materials. The invention also relates to flip chip-type semiconductor devices sealed with such sealants.
2. Prior Art
The trend toward smaller sizes, lighter weights and increased capabilities in electrical equipment has led to a shift in the dominant semiconductor mounting process from pin insertion to surface mounting. One bare chip mounting technique is flip chip (FC) mounting, which involves forming anywhere from several electrodes to several thousand electrodes called xe2x80x9cbumpsxe2x80x9d about 10 to 100 xcexcm in height on the interconnect pattern side of a large-scale integration (LSI) chip, and bonding the substrate electrodes with a suitable material such as a conductive paste or solder. The sealing materials (or sealants) used for flip chip protection must be introduced into small gaps only a few tens of microns in size between the substrate and the bumps and other features on the LSI chip. Prior-art liquid epoxy resin compositions used as underfill materials in flip chips are comprised of an epoxy resin, a curing agent and an inorganic filler. It is generally the practice today to include in such compositions a large amount of inorganic filler so as to give the sealant a linear expansion coefficient which agrees with those of the semiconductor chip, the substrate and the bumps, thereby increasing device reliability.
Yet, although stress properties are no longer a problem in flip chip underfill materials having high loadings of such fillers, the higher filler content has increased the viscosity of the composition. The increased viscosity dramatically lowers the speed at which the composition penetrates the gap between the chip and the substrate, greatly reducing production efficiency. A desire has thus been felt for some way of overcoming this problem.
It is therefore an object of the invention to provide a sealing material (or sealant) or, more precisely, an underfill material, for flip chip-type semiconductor devices which contains a large amount of inorganic filler, yet has a low viscosity, allowing it to penetrate into small gaps. Another object of the invention is to provide a flip chip-type semiconductor device sealed with such a sealing material (or sealant).
The inventor has found that the formulation of (A) a liquid epoxy resin, (B) an optional curing agent, (C) an inorganic filler, and (D) 1 to 15 parts by weight of a microencapsulated catalyst per 100 parts by weight of component A alone (if component B is not included) or components A and B combined (if component B is included) provides sealing materials (or sealants) which have an excellent stability at high temperatures. Such sealants, in spite of containing a large amount of inorganic filler, can be brought to a low viscosity by elevating the temperature of the semiconductor device and can thus be introduced into small gaps, making them effective as underfill materials, particularly in large-die flip chip-type semiconductor devices. These properties are especially manifest when the microencapsulated catalyst serving as component (D) contains an imidazole compound and/or an organophosphorus compound, has an average particle size of 0.5 to 15 xcexcm, and has a catalyst dissolution from the microcapsules into o-cresol, as measured at 30xc2x0 C. over a period of 15 minutes, which corresponds to at least 70% by weight of the total amount of catalyst in the microcapsules.
It thus became clear to us that liquid epoxy resin composition-type sealing materials for flip-chip semiconductor devices have excellent thin-film penetration properties and shelf stability, particularly as underfill materials, and are capable of endowing semiconductor devices in which they have been used with exceptionally high reliability.
Accordingly, the invention provides a sealing material for flip chip-type semiconductor devices, which sealing material comprises a liquid epoxy resin composition that includes:
(A) a liquid epoxy resin,
(B) an optional curing agent
(C) an inorganic filler, and
(D) a microencapsulated catalyst.
The amount of the microencapsulated catalyst is 1 to 15 parts by weight per 100 parts by weight of component A alone (if component B is not included) or components A and B combined (if component B is included).
Preferably, the microencapsulated catalyst contains an imidazole compound and/or an organophosphorus compound, has an average particle size of 0.5 to 15 xcexcm, and has a catalyst dissolution from the microcapsules into o-cresol, as measured at 30xc2x0 C. over a period of 15 minutes, which corresponds to at least 70% by weight of the total amount of catalyst in the microcapsules.
The invention additionally provides a flip chip-type semiconductor device sealed with such a sealing material.